[Tigga]

late to this convversation but some good comments on this video...

Do you need two chargers at home for two EVs?

Multi-EV households are becoming more common. So, should you get two charge points installed at home or can you manage with one? Our guide has the answers.

www.smarthomecharge.co.uk

short answer is for most people share a single point; alternate charging days! if you really need it, you might need 3phase! (as commented above)
BUT there are chargers like wallbox that can talk to eachother and share the loading of each charger; or if on separate circuits you can have configuations which thottle the load based upon total demand.

 

[barneyd]

But what if the OP has a family emergency and has to drive to Edinburgh at a moments notice, towing a caravan?

There must be a massive traffic jam in Edinburgh with all the people who couldn’t possibly have an EV for exactly that reason.

 

[EricM]

Yes. And no. You can only have the amount your incoming fuse is rated for. And I’ve not seen one rated at more than 100A on a single phase supply. More may be possible, but I’ve never come across one.

Of that 100A you can take up to 32A for the 7.4kW charger. If you add a second charger on the same 100A main fuse, you will have two chargers running at 3.6kW, which is better than nothing, but not a great advance on the 2.4kW most granny chargers give you.

One 7kW charger will need 30A; two would need 60A. If your property has a 100A supply that would still leave 40A (around 10kW) available for other uses. Very few houses actually use 10kW at any instant and if you were wanting to do your charging between (say) MN & 6am you might even be able to run 3 chargers (90A) at once with the remaining 10A being enough for a small background load.

 

[wja96]

One 7kW charger will need 30A; two would need 60A. If your property has a 100A supply that would still leave 40A (around 10kW) available for other uses. Very few houses actually use 10kW at any instant and if you were wanting to do your charging between (say) MN & 6am you might even be able to run 3 chargers (90A) at once with the remaining 10A being enough for a small background load.

Your commitment to an aggressive diversity calculation does you credit, but your home won’t meet any kind of wiring regulations if you specify it like that.

If you look at the fuses in your consumer unit they look massive. And yet they still trip and even blow completely on occasion.

Every circuit in your home has a specification set out in the current version of the wiring regulations and the EVSE installers have to comply with the latest version on any work they do irrespective of when the property was constructed.

So if you have a gas boiler and a gas cooker your 32A cooker circuit probably looks like massive overkill but if you have an electric hob and an electric oven when you cook Christmas dinner with it all switched on, you may actually exceed the rating in the circuit while you heat the oven(s) up.

And let’s hope you don‘t live anywhere with an electric shower. Or night storage heaters!

There is some allowance for the fact that everything isn’t switched on at once (diversity in demand calculation) but the required specifications are still massively over what you’d think you actually use. That’s why you have a 60A fuse in the first place. Because you might turn everything on at once.

There is zero diversity allowed on an EVSE and any installer will look at your 60A circuit and just say no. No install possible. Even on an 80A circuit they might limit you to 16A or 30A rather than the full 32A. Andersen will not allow one of their authorised installers to install an Andersen EVSE on a circuit fused at less than 100A.

So while you may be correct, you won’t get a qualified installer to do what you suggest. You can’t have two 7.4kW EVSEs charging on a 100A fused single phase supply. You get two sharing 7.4kW which typically means 3.6kW each.

If you install them yourself your theoretical calculations may be correct, and I hope they are because the energy required to melt a 100A fuse will be pretty spectacular to behold.

If you want to charge two cars at 7.4kW you pretty much need a 3-phase supply. At which point you can charge two cars at 11kW. Which is rather lovely.

 

[EricM]

Your commitment to an aggressive diversity calculation does you credit, but your home won’t meet any kind of wiring regulations if you specify it like that.

If you look at the fuses in your consumer unit they look massive. And yet they still trip and even blow completely on occasion.

Every circuit in your home has a specification set out in the current version of the wiring regulations and the EVSE installers have to comply with the latest version on any work they do irrespective of when the property was constructed.

So if you have a gas boiler and a gas cooker your 32A cooker circuit probably looks like massive overkill but if you have an electric hob and an electric oven when you cook Christmas dinner with it all switched on, you may actually exceed the rating in the circuit while you heat the oven(s) up.

And let’s hope you don‘t live anywhere with an electric shower. Or night storage heaters!

There is some allowance for the fact that everything isn’t switched on at once (diversity in demand calculation) but the required specifications are still massively over what you’d think you actually use. That’s why you have a 60A fuse in the first place. Because you might turn everything on at once.

There is zero diversity allowed on an EVSE and any installer will look at your 60A circuit and just say no. No install possible. Even on an 80A circuit they might limit you to 16A or 30A rather than the full 32A. Andersen will not allow one of their authorised installers to install an Andersen EVSE on a circuit fused at less than 100A.

So while you may be correct, you won’t get a qualified installer to do what you suggest. You can’t have two 7.4kW EVSEs charging on a 100A fused single phase supply. You get two sharing 7.4kW which typically means 3.6kW each.

If you install them yourself your theoretical calculations may be correct, and I hope they are because the energy required to melt a 100A fuse will be pretty spectacular to behold.

If you want to charge two cars at 7.4kW you pretty much need a 3-phase supply. At which point you can charge two cars at 11kW. Which is rather lovely.

Why the reference to a 60A fuse ?

OP never mentioned having one and I was specifically considering the case where a 100A fuse was fitted

I was assuming that each EVSE would be wired back to its own 30A (more likely 32A) fuse and indeed that you'd never want to run them when there was any chance of using other high current devices.

 

[Slartibartfast]

Here it is common for main fuses to be 60A or even 40A and ours used to be 40A before the whole shebang was upgraded a few years ago. We installed an electric shower and the bloke that did it fitted a shower priority box that stopped the risk of the fuse blowing if we used the shower. These shower boxes were common here and they work just as well with electric car chargers I have been told.

I cannot see any problem with just having to manage the load like this as it has been shown here to be safe as the things have been around at least 20 years and I have never heard of them causing any problem. The way ours used to work was that it either supplied electricity to the shower or it supplied electricity to the stove but not both at once and if the shower was being used the cooker was dead and would not come back on until the shower was turned off. That shower used more electricity than a charger I am sure and as most people charge at night when they are not likely to be using the stove at the same time so it would not even be something that was noticed.

 

[Scrooge]

But what if the OP has a family emergency and has to drive to Edinburgh at a moments notice, towing a caravan?

Use a local rapid, got to be cheaper for the odd occasion

 

[wja96]

Why the reference to a 60A fuse ?

OP never mentioned having one and I was specifically considering the case where a 100A fuse was fitted

I was assuming that each EVSE would be wired back to its own 30A (more likely 32A) fuse and indeed that you'd never want to run them when there was any chance of using other high current devices.

It’s a simple example of how the current wiring regulations prohibit doing what you suggest even though, according to your calculation, you have capacity for it. According to you, you could run two 30A EVSEs on a 60A supply and 3 on a 100A fused supply. You just can’t. The wiring regulations don‘t allow it. Even with an 80A incoming fused supply the DNO may choose not to allow the installation unless the diversity has been calculated and the installer can justify it to them.

Even with a 100A fused incoming supply you only just have capacity for one 32A fused EVSE because the competent electrical installer cannot apply any amount of diversity discount on that supply. This also applies to anything on a cooking, heating or shower circuit.

And as for being able to control what loads are present in your home, the wiring regulations don’t give you that opportunity.

 

[Ambassador Spock]

Here it is common for main fuses to be 60A or even 40A and ours used to be 40A before the whole shebang was upgraded a few years ago.

We got super lucky when we had our Zappi installed about a month ago - the Zappi tech came for the site survey and said he wasn't allowed to pull the fuse to see whether it was 60a or 80a, and so he'd have to lower the Zappi to 16a (in the software) when he installed it "just in case". The next day I happened to see a Western Power Distribution truck next-door, so I went out and spoke with the guy. He finished up the job he was there for and came to take a look. Our main fuse was indeed 60a, but he had a spare 80a on the truck and just replaced it then and there! I don't know how common that was, but it sure seemed nice to us!

 

[wja96]

Here it is common for main fuses to be 60A or even 40A and ours used to be 40A before the whole shebang was upgraded a few years ago. We installed an electric shower and the bloke that did it fitted a shower priority box that stopped the risk of the fuse blowing if we used the shower. These shower boxes were common here and they work just as well with electric car chargers I have been told.

I cannot see any problem with just having to manage the load like this as it has been shown here to be safe as the things have been around at least 20 years and I have never heard of them causing any problem. The way ours used to work was that it either supplied electricity to the shower or it supplied electricity to the stove but not both at once and if the shower was being used the cooker was dead and would not come back on until the shower was turned off. That shower used more electricity than a charger I am sure and as most people charge at night when they are not likely to be using the stove at the same time so it would not even be something that was noticed.

Obviously this is an international forum and the UK has regulations that prohibit some things which are allowed in other countries. The fact that the electrical regulations have to be applied to buildings and installations that pre-date them and electricians effectively have an incentive to upgrade older electrical installations means that cheaper, simpler, but equally safe and effective options are not available in the UK.

The UK also suffers from having a national grid to dwellings based on a single-phase supply. Other countries (especially where people tend to build their own home) or that have poor mains gas provision often have 3-phase power supplies in their homes already because if you’re running an 8.5kW or 11kW shower at the same time as you’re boiling a 3kW kettle and a 1.5kW toaster and a 2kW hair dryer and you’ve got a few lights on, then you’ll easily exceed the fused supply on a building.

And if you have storage heating then those heaters will be warming at 16A each just when everyone says they want to charge their cars.

And actually, many EVSEs sold have current management built-in. Certainly Pod-Point have a clamp on the supply and will throttle the charger back if it detects high load in the house.

 

[Slartibartfast]

Our regulations are just a dressed up and rewritten version of the UK regulations so are close to being exactly the same and I know for sure that priority boxes are used just over the border in the six counties so they must meet the UK version of the regulations.

I also know for sure that Tesla chargers can do exactly the same thing as we have installed loads of them on sites with restricted supplies and they talk to each other and keep the load down to a safe limit in the same way that a priority box does with a shower and stove. We installed a bunch of Tesla chargers at a hotel that were connected up so only half of them could work at any one time they were just wired as pairs from the supply so only one of the pair could be charging at any time and as soon as a car was charged the chargers would switch over and start charging the other one. That was about 3 years ago so this is not anything new.

I know that the shower priority box we had left over after our supply was upgraded by ESB a few years ago has been reused over the border for a charger as the bloke that fitted our charger asked if he could have ours to reuse for another customer on the UK side who only had a limited supply coming into his house and as that electrician is a pretty smart fella I can not believe that he was breaking any rules.

 

[Jeremy Harris]

Your commitment to an aggressive diversity calculation does you credit, but your home won’t meet any kind of wiring regulations if you specify it like that.

If you look at the fuses in your consumer unit they look massive. And yet they still trip and even blow completely on occasion.

Every circuit in your home has a specification set out in the current version of the wiring regulations and the EVSE installers have to comply with the latest version on any work they do irrespective of when the property was constructed.

So if you have a gas boiler and a gas cooker your 32A cooker circuit probably looks like massive overkill but if you have an electric hob and an electric oven when you cook Christmas dinner with it all switched on, you may actually exceed the rating in the circuit while you heat the oven(s) up.

And let’s hope you don‘t live anywhere with an electric shower. Or night storage heaters!

There is some allowance for the fact that everything isn’t switched on at once (diversity in demand calculation) but the required specifications are still massively over what you’d think you actually use. That’s why you have a 60A fuse in the first place. Because you might turn everything on at once.

There is zero diversity allowed on an EVSE and any installer will look at your 60A circuit and just say no. No install possible. Even on an 80A circuit they might limit you to 16A or 30A rather than the full 32A. Andersen will not allow one of their authorised installers to install an Andersen EVSE on a circuit fused at less than 100A.

So while you may be correct, you won’t get a qualified installer to do what you suggest. You can’t have two 7.4kW EVSEs charging on a 100A fused single phase supply. You get two sharing 7.4kW which typically means 3.6kW each.

If you install them yourself your theoretical calculations may be correct, and I hope they are because the energy required to melt a 100A fuse will be pretty spectacular to behold.

If you want to charge two cars at 7.4kW you pretty much need a 3-phase supply. At which point you can charge two cars at 11kW. Which is rather lovely.

Just to be absolutely clear, there is nothing within BS7671:2018 Amendment 1 that prohibits the connection of two 7 kW charge points to a single phase 80 A or 100 A fused incoming supply. Neither does BS7671:2018 contain any specific regulation of how diversity should be applied, that is only guidance contained within the On Site Guide. There is nothing within the current edition of the OSG that gives guidance as to how to apply diversity of calculate total demand in the case of EVSE installations.

Common sense is expected to be applied and there is an obligation on the installer to calculate or measure a realistic maximum demand based on what he/she can see and measure on the installation. The way that this should be done is to put a monitor on the existing installation for a reasonable period (24 hours minimum, ideally about 7 days) to determine the pattern of usage, peak demand and demand duration and then determine whether it would be safe to connect any given additional load.

In practice, few domestic installations come anywhere close to reaching the maximum their supply can provide. I measured ours and we are close to being a worst case, as the house has electric heating, electric water heating and cooking and has no other form of energy at all (no gas, no oil and no solid fuel appliances). Our peak demand before I energised our two charge points was 31 A from an incoming single phase supply to the main fuse that is a 4m run of 35mm² concentric connected to a 95mm² run of Wavecon from the sub-station and that goes on to feed two other properties in the valley. We have a 100 A fuse in the cut out and the incoming Al/Cu 35mm² concentric is rated at 100 A.

I had absolutely no problem in installing two charge points to our supply and have enough evidence to prove that the total demand that was measured and assessed before installation complies with the regs. As it happens I did install a re-purposed remote generator changeover switch so that only one of the two charge points is energised at any one time, but this was complete overkill as we only every charge overnight and the overnight demand from the rest of the house never exceeds 5 kW (that is with the heat pump on maximum and the water heating on). Even without the changeover switch and with both cars charging at 7 kW we would still be comfortably within the maximum rating of the incoming supply, with a total demand of about 82 A or so. FWIW, a 100 A BS88 incomer fuse will not ever blow at up to about 150 A overload, it will just get a bit warm. At 200 A a 100 A BS88 fuse will take about 300s to blow.

I'm not for a moment suggesting that anyone try and run their installation right at the limit, but there is provision within the distribution system that means it is tolerant to some very high overload conditions without failing. A good example would be a cannabis grow not far from here that I looked at after the police had removed all the stuff. They had tapped into a fairly hefty supply (and must have been live working when they did it) but had only used thin cables to the grow sheds, 16mm² SWA, that they had torpedo jointed to a run of 95mm² wavecon. They were pulling around 150 A continuously from that supply, with no fuses at all, and although buried 16mm² SWA is only rated at 119 A there was no indication of any damage to the cable. The grow farm had been running for well over a year according to the police with the lights, pumps and fans running 24/7.